Solid-state imaging systems or imaging readers have been used, in both handheld and hands-free modes of operation, to electro-optically read targets, such as one-dimensional bar code symbols, particularly of the Universal Product Code (UPC) type, each having a linear row of bars and spaces spaced apart along a scan direction, as well as two-dimensional symbols, such as Code 49, which introduced the concept of vertically stacking a plurality of rows of bar and space patterns in a single symbol, as described in U.S. Pat. No. 4,794,239. Another two-dimensional code structure for increasing the amount of data that can be represented or stored on a given amount of surface area is known as PDF417 and is described in U.S. Pat. No. 5,304,786.
The imaging reader includes an imaging module having a solid-state imager with a sensor array of photocells or light sensors, which correspond to image elements or pixels in a two-dimensional field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the symbol being imaged, and for projecting the return light onto the sensor array to initiate capture of an image of the symbol as pixel data. The imager may be a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and includes associated circuits for producing and processing electrical signals corresponding to a one- or two-dimensional array of the pixel data over the field of view. The imager captures the return light under the control of a controller or programmed microprocessor that is operative for processing and decoding the electrical signals into data indicative of the symbol being imaged and read. During operation, the controller selectively energizes selected sensors and, in effect, maps or draws at least one virtual scan line across the symbol, in a manner analogous to a real scan line of a moving laser reader or laser scanner also operative for electro-optically reading such symbols.
It is therefore known to use the imager for capturing a monochrome image of the symbol as, for example, disclosed in U.S. Pat. No. 5,703,349. It is also known to use the imager with multiple buried channels for capturing a full color image of the symbol as, for example, disclosed in U.S. Pat. No. 4,613,895. It is common to provide a two-dimensional CCD with a 640×480 resolution commonly found in VGA monitors, although other resolution sizes are possible.
In certain design of imaging readers, high resolution solid-state imagers are used. For example, a solid-state imager can have a resolution of 1280×960 pixels or more. In certain applications, the solid-state imager may need to output images at a relatively frame rate of, for example, about 30-60 frames per second. The higher frame rate allows the imager to effectively capture images of fast-moving objects. Outputting high resolution images at high frame rated may impose large bandwidth requirement. In certain applications, it may be necessary to reduce the resolution of the output images transmitted to a decoder from the solid-state imager. The resolution of the output images can be reduced by sub-sampling the original images. For example, if one column is selected for each two columns in the original images and one row is selected for each two rows in the original images, the resolution of the output images can be reduced from the original images by a factor of 2×2. But reductions by factors of 2 or higher could pose more severe limitations than downstream image analysis software can handle. In certain applications, it is desirable to reduce the resolution of the output images from the original images by a fractional ratio, such as, by a factor of 3/2×3/2, as a compromise between higher resolution images and higher frame rates.